<p>One of the most common volatile organic compounds (VOCs) group is monoterpenes. Monoterpenes share the molecular formula C10H16, they are usually cyclic and have a pleasant smell. The most common monoterpenes are limonene (present in citrus fruits) and α-pinene (present in conifers&rsquo; resin). Different monoterpenes have different chemical, biological and ecological properties thus it is experimentally very important to be able to differentiate between them in real time. Real time instruments such as Proton Transfer Reaction-Time of Flight-Mass Spectrometry (PTR-ToF-MS), offer a real time solution for monoterpene measurement but at the cost of selectivity resulting in all monoterpenes being seen at the same m/z. In this work we used Selective Reagent Ion-Time of Flight-Mass Spectrometry (SRI/PTR-ToF-MS) in order to explore the differences in ion branching when different ionizations (H3O+, NO+ and O2+) and different drift tube reduced field energies (E/N) were used. We report a comprehensive ion library with many unique features, characteristic for individual monoterpenes.</p>

<p>Here we introduce a new prototype of a Proton Transfer Reaction-Time-Of-Flight Mass Spectrometry (PTR-TOFMS) instrument. In contrast to commercially available PTR-TOFMS devices so far, which utilize a transfer lens system, the novel prototype is equipped with a quadrupole ion guide for the highly effective transfer of ions from the drift tube to the mass spectrometer; hence we call it PTR-QiTOF, whereas &ldquo;Qi&rdquo; stands for &ldquo;Quadrupole interface&rdquo;. This new interface greatly improves the TOF mass resolution because of favorable injection conditions. Depending on whether we optimize the PTR-QiTOF to maximum sensitivity or maximum mass resolution, we get about 6900 and 10,400 m/m mass resolution, respectively, already at m/z 149 (increasing with ascending masses). Furthermore, we increase the pressure in the drift tube from typically 2.2 mbar to 3.8 mbar and the drift tube voltage from 600V to 1000 V. We directly compare the sensitivities of a commercial state-of-the-art PTR-TOFMS instrument to this &ldquo;high pressure&rdquo; PTR-QiTOF prototype and find that these modifications lead to a gain on average by a factor of 25 in terms of sensitivity with a maximum of about 4700 cps/ppbv for dichlorobenzene atm/z 147 for the PTR-QiTOF. This is (to our knowledge) the highest sensitivity ever reported for a PTR-MS instrument, regardless of the employed mass spectrometer. The increased sensitivity also has a very positive effect on the detection limit, which lies now at about 20 pptv with 100ms and 750 ppqv after 1 min integration time.Weprovide data on the linearity of the instrumental response over a concentration range of five orders of magnitude and evaluate the prototype&rsquo;s performance in a real-life test by analyzing the dynamic headspace of a minute amount of trinitrotoluene using only 2 s integration time.</p>

<p>Abstract Proton transfer reaction-mass spectrometry (PTR-MS) has successfully been applied to a wide variety of food matrices, nevertheless the reports about the use of PTR-MS in the analysis of alcoholic beverages remain anecdotal. Indeed, due to the presence of ethanol in the sample, PTR-MS can only be employed after dilution of the headspace or at the expense of radical changes in the operational conditions. In the present research work, PTR-ToF-MS was coupled to a prototype FastGC system allowing for a rapid (90&nbsp;s) chromatographic separation of the sample headspace prior to PTR-MS analysis. The system was tested on red wine: the FastGC step allowed to rule out the effect of ethanol, eluted from the column during the first 8&nbsp;s, allowing PTR-MS analysis to be carried out without changing the ionization conditions. Eight French red wines were submitted to analysis and could be separated on the basis of the respective grape variety and region of origin. In comparison to the results obtained by direct injection, FastGC provided additional information, thanks to a less drastic dilution of the sample and due to the chromatographic separation of isomers. This was achieved without increasing duration and complexity of the analysis.</p>

Abstract Proton-transfer-reaction time-of-flight mass spectrometry has been employed in a 12&#xa0;months breath gas analysis study to describe the breath composition of 19 cigarette smoking and 53 non-smoking women. The most prevalent constituents were acetone (1.8&#xa0;ppmv), methanol (310&#xa0;ppbv), isoprene (280&#xa0;ppbv), ethanol (130&#xa0;ppbv), acetaldehyde (90&#xa0;ppbv) and acetic acid (70&#xa0;ppbv). Smokers showed the largest signal increase in acetonitrile (ratio smoker/non-smoker 29), benzene (ratio 11), 2-methylfuran (ratio 8) and 2,5-dimethylfuran (ratio 7). Calibration gas measurements allowed the instruments performance regarding precision and accuracy of ion mass-to-charge, m/z, and concentration accuracy measurement to be assessed. The standard deviation of the concentration measurements was 14% or smaller (with the exception of ethanol) with no trend in this variation of sensitivity. The limit of detection (LOD) lay in the sub ppbv range, based on an integration time of 2&#xa0;s. The m/z accuracy was better than 0.0016 (or less than 29&#xa0;ppm of the ion mass) throughout the study. The standard deviation of the measured m/z was less than 0.0025 and the coefficient of variation was less than 29&#xa0;ppm. Keywords PTR-TOF-MS, Smokers’ breath, Breath volatile organic compounds, \{VOCs\}

<p>Abstract Following up the first introduction of an advanced proton-transfer-reaction mass spectrometry (PTR-MS) instrument in 2012, which is capable of utilizing H3O+, NO+, O2+, and Kr+, respectively, for chemical ionization and subsequent detection of a broad variety of compound classes, here we present calculations of the best suitable mixing ratios between the sample and buffer gas in Kr+ mode, as well as two possible applications of such an instrument in indoor air analysis and engine exhaust studies. Due to secondary reactions in the drift tube the admixing of a buffer gas with a higher recombination energy than Kr+ is inevitable. The calculations show that though a dilution ratio of 1:40 (sample : buffer gas) results in the highest sensitivity, for accurate substance quantification a dilution ratio of at least 1:500 is necessary. By applying this theoretical knowledge to two practical examples, we find that the quantification of CH4, CO, O2, and CO2, respectively, is well within the range of the expected concentrations. We conclude that such an instrument can be of utmost benefit for researchers working for example in environmental research, because in H3O+ mode volatile organic compounds can be quantified with very high sensitivity and low detection limits and by means of switching the reagent ions to Kr+ additional instrumentation for quantification of (inorganic) pollutants becomes virtually obsolete.</p>

The storage capability of Tedlar(R) bags for gaseous compounds was assessed using on-line proton-transfer-reaction mass spectrometry (PTR-MS). Sample bags were filled with a mixture of volatile organic compounds (VOCs) at known quantities in the ppbv range. The test gas included alcohol, nitrile, aldehyde, ketone, terpene and aromatic compounds. PTR-MS enabled frequent bag-direct measurements of compound abundances over a 70 h storage period. Concentrations of all compounds decreased with bag storage time, with compound-specific decay rates. The most rapid decline in concentration levels was seen for water vapour in the bag, i.e. sample humidity. Such a decrease is particularly relevant for breath-gas samples, where water vapour content is high. Compound losses were attributed to a combination of adsorption to and diffusion through the bag walls. Storage property observations suggest that sample analyses made within 10 h of sampling offer adequate sample authenticity replication. Based on observations, an appropriate bag-cleaning procedure was established and assessed. Results indicated that acceptable bag cleanliness for breath-gas sampling is achievable.

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